Asking Forgiveness
Question
If I did an aveira to someone, but they forgot about it, can I still ask them mechila, even though they'll have have no recollection of what I did.
Answer
Shalom!
Thank you for your question.
Your question is quite similar to the following.
There is a dispute among the authorities about what to do when one person spoke Lashon Hara about a second person, but the second person has no idea that Lashon Hara was spoken about him.
Rav Yisroel Salanter famously ruled that if by telling the second person that you spoke Lashon Hara about them you will cause them pain and sadness then one should not do so. Instead, one should do extra Teshuva to Hashem and try to speak good about that person in the future.
On the other hand, the Chofetz Chaim (Hilchos Lashon Hara 4:12) ruled that it is only possible to achieve full teshuva if the person forgives you for what you did. Hence, according to this approach, one is required to reveal to them what one has said and then ask forgiveness even if it will cause them harm or pain.
According to halacha, we say that if telling your friend about the lashon hara or what you did to him will cause him pain, then it is better not to tell him. Unless you know that it would no longer bother him, in which case you should approach him and ask for forgiveness.